Technical Report Investigation of micro/meso sheet soft punch stamping process – simulation and experiments Linfa Peng a , Peng Hu a , Xinmin Lai a, * , Deqing Mei b , Jun Ni c a State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, 800# Dong Chuan Road, Shanghai 200240, China b Department of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China c Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor, MI 48109, USA article info Article history: Received 4 September 2007 Accepted 30 May 2008 Available online 12 June 2008 abstract Different form traditional forming process, sheet soft punch process uses only a rigid die and the other tool set is a flexible medium, such as natural or synthetic rubbers. In this study, a kind of micro/meso sheet soft punch stamping process to fabricated micro channels is investigated via numerical simulations and experiments. Plane strain finite element analysis (FEA) models of different channel geometry (h=w) are established to analyze the significant parameters associated with this process. Grain size of sheet metal and some key process parameters, such as the hardness of soft punch and lubricant condition, are detailed studied in this paper. Finally, the numerical results are partly validated by experiments. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction With the requirements of the miniaturization in electronics and other mini devices, there is a growing demand for micro parts. As a mass production manufacturing technique, micro/meso forming processes have recently attracted the attention of the manufactur- ers and researchers [1–10]. Micro-sheet forming is the main pro- cess to manufacture micro-sheet parts due to its low cost, small space taking, low energy consuming. However, traditional rigid die and punch forming technology need much time to design the process and tools. Moreover, the accurate assembly of rigid die, punch and other attachments is also very complex so that the clearance of tools can be accurately kept in order to avoid defects such as wrinkling and rupture. Moreover, the miniaturization of tools and process make it more difficult to design and manufacture them. Comparing with traditional sheet forming process with rigid die set, micro/meso sheet forming processes by soft punch have many advantages. It only utilizes a rigid die, and the punch is soft materials such as natural or synthetic rubbers (shown in Fig. 1). Therefore only rigid punch must be designed and accurately man- ufactured; also there is no problem in the precise assembly of soft punch and rigid die. Therefore, the time and cost can be greatly reduced. In this field, former researchers have done some work. David and Emil [11] presented an experimental study of the rubber form- ing process in order to produce sheet metal components. They investigated the capability of the process and optimized the pro- cess parameters to ensure defect-free products by using a 100 t double-acting hydraulic press. Husnu [12] studied the significant parameters associated with FFP (flexible forming process) by numerical simulation with a commercially available finite element package. Their investigations showed the effectiveness of finite ele- ment simulations in process design and exposed the rubber hard- ness and its advance, blank material type, contact friction, die design as crucial parameters that require adjustment before actual operations. Giuseppe [13] also optimized the process with numer- ical simulation and experiments, Thiruvarudchelvan [14] pre- sented several kinds of flexible forming processes to produce sheet metal ashtrays and plates. Furthermore, he presented the principles concerned with this technique, such as design of the ure- thane pads and actual prototype devices, in his study. However, with the decreasing of scale, the so called size effects make the know-how of traditional forming process can not be di- rectly used [1,2,7–8,15] in micro/meso forming field. The principles of micro forming technique are not clearly revealed, to say nothing of micro sheet forming process by utilizing soft punch. Those crit- ical process parameters related with the quality of workpiece have not been fully studied. The main purpose of this paper is to establish a finite element analysis (FEA) model to study sheet forming process using soft punch at micro/meso scale. Hyper-elastic material model is de- fined for soft punch and discrete rigid elements for rigid die. Therefore the plane strain FEA model is established for the simu- lations of forming process. Grain size of sheet metal and some key process parameters, such as the hardness of soft punch and lubri- cant condition, are detailed studied in this paper by using the FEA simulations. The results are partly confirmed by the forming experiments. 0261-3069/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2008.05.074 * Corresponding author. E-mail address: xmlai@sjtu.edu.cn (X. Lai). Materials and Design 30 (2009) 783–790 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes